Wearable devices, such as watches and fitness tracking devices, are essentially a small computing device and becoming more popular with users. Generally, a wearable watch device can be used in the traditional sense to track time, and may be used for communication with a user's mobile phone, such as to display received messages, incoming phone calls, calendar appointments, and generally as an extended interface of the mobile phone. Other types of wearable devices that are increasingly popular are fitness tracking and feedback devices that can be implemented with sensors to monitor the heartrate of a user, distance traveled, exercise levels, sleep patterns, and other activities, movement, and personal metrics of a user wearing the device.
Some wearable devices are designed to obtain electrocardiogram (ECG) readings, which provide the user with a reading of heart rate over time and can be used to diagnose potential heart issues. An ECG measures the electrical signal between two extremities, such as from one hand to the other hand, with the electrical signal passing through the heart between the two extremities. Generally, the accuracy and quality of the ECG signal is related to the surface area of the two contacts between which the electrical signal passes, and implementation in a small form-factor wearable device does not provide a reliable ECG reading.